If we got a "Reached the end of the CPU serial log without finding a
result" because the test phase timed out, then the CPU serial would have
been closed as part of the timeout process, so we need to close the rest
and re-instantiate the servo run class.
fastboot and poe already re-instantiate the class on retry.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17689>